Issa, Amine

Spinal cord hemisection at C2 (SH) disrupts descending drive to ipsilateral phrenic motoneurons (PMNs) causing unilateral diaphragm muscle (DIAm) paralysis. Previously, we found a decrease in motoneuron size at 2 weeks post‐SH. Recently, we found neuregulin (NRG) in synaptic boutons surrounding PMNs. NRG is a trophic factor known to regulate development of the neuromuscular junction, but the effect of NRG on motoneurons is unknown. We hypothesized that 1) NRG input to PMNs is supraspinal in origin, and 2) SH disrupts NRG input to PMNs. Adult male Sprague‐Dawley rats underwent SH or sham‐surgery. PMNs were retrogradely labeled by intramuscular injection of Alexa488‐conjugated cholera toxin B. Using laser capture microdissection, we found that PMNs express mRNA for the NRG receptors ErbB2 and ErbB3, providing a functional substrate for a NRG effect. Two weeks post‐SH, labeled PMNs and NRG boutons were imaged using confocal microscopy. PMN morphology and the number of NRG boutons in the vicinity of PMNs were determined using a computerized, semi‐automated reconstruction algorithm. NRG boutons were fairly homogeneously distributed on motoneurons independent of size. Following SH, few NRG boutons were observed. We conclude that 1) NRG input to PMNs derives from a supraspinal source; and 2) SH removes NRG input to PMNs. It is possible that NRG input exerts a trophic influence on PMNs. Supported by NIH grants HL37680, AR51173 and Mayo Clinic

Neuregulin (NRG) is a nerve derived trophic factor that regulates acetylcholine receptor expression during neuromuscular junction development. NRG also has important trophic effects in the adult central nervous system. We hypothesized that NRG is a trophic factor for phrenic motoneurons. In adult male Sprague‐Dawley rats, we examined NRG‐1 immunoreactivity in the vicinity of phrenic motoneurons. Retrogradely‐labeled phrenic motoneurons were imaged and reconstructed in 3D. NRG‐1 boutons were found mainly around the soma and primary dendrites. The co‐localization of NRG boutons and synaptic markers was determined using multicolor confocal microscopy and a custom‐developed application (Metamorph; Universal Imaging). We found that 94 ± 3% of NRG‐containing boutons resided on synapses, as determined by co‐localization with synaptophysin. In addition, 6 ± 3% of synapses on phrenic motoneurons (within 1 micrometer of soma and primary dendrite surface) expressed NRG. Overall, 13 ± 5 NRG boutons were present at the soma vs. 6 ± 3 at each primary dendrite of a motoneuron.Thus, 57% of NRG‐containing boutons were surrounding the motoneuron soma. In summary, NRG‐1 synaptic boutons are present at phrenic motoneurons in the adult, although its role is presently unknown. Supported by NIH grant AR51173.

Retrograde transport of fluorescent dyes permits imaging of nearly the entire pool of motoneurons when administered in the target muscle or axon shaft, but the extent of dendritic labeling is usually limited. We used an intracellular injection of Lucifer Yellow CH (LY) into retrogradely labeled phrenic motoneurons (PMNs) to enhance dendritic structure. PMNs were specifically labeled by Alexa Fluor 488‐conjugated cholera toxin fragment B (CTB) injected into the pleural space of 18‐days old rats. After a 72‐hr survival period, animals were transcardially perfused with 4% paraformaldehyde and 4% sucrose in 0.1 M phosphate buffer. Cervical spinal cords were sectioned in coronal plane. Individual CTB‐labeled PMNs were intracellularly injected with LY under direct visual control and subsequently imaged with an Olympus FluoView 200 laser‐scanning confocal system. Image processing and analyses were performed using Metamorph 7.4 software. PMNs were extensively labeled and reconstructed in 3D. The range of visible primary, secondary and tertiary processes was 3 ‐ 7, 2 ‐ 4 and 0 ‐ 2 per PMN, respectively. Average length of a single dendritic tree was 218.0±20.1 μm and surface area was 1295±199 μm 2 . The described technique provides 3D quantitative morphometry of a large sample of retrogradely‐labeled PMNs in great detail. Supported by NIH grants HL37680 and AR51173.

Background Whether lung fluid accumulates in acclimating individuals at high altitude (HA) remains controversial. Purpose To assess the effect of HA on lung fluid regulation. Methods/Results Systolic pulmonary artery pressure (sPAP) (echo), lung diffusing capacity for CO (DLCO), pulmonary capillary blood volume (Vc), alveolar‐capillary conductance (Dm) (single breath method), ultrasound lung comets (ULCs) and pulmonary function (PFTs) were assessed in 8 healthy adults at sea‐level and after 1 and 9 days at Mt. Everest Base Camp (EBC), Nepal (5150 m). Also, after 5 days at EBC, DLCO and PFTs were assessed in 5 subjects pre‐and post‐acute albuterol administration. EBC was reached after an 8 d hike at progressively increasing altitudes starting at 2800 m. Altitude exposure increased sPAP, had no effect on DLCO, increased Dm and decreased Vc with a subsequent increase in Dm/Vc, and decreased the number of ULCs (Table 1). There was no change in FVC or FEV 1 but an increase in MEF 50 . Albuterol administration increased PEF (11.85±1.52 vs. 12.40±1.45 L/s) and MEF 50 (4.85±0.77 vs. 6.00±1.30 L/s) but had no effect on DLCO, Dm or Dm/Vc. Conclusion These data suggest that lung fluid is decreased in acclimating healthy humans at high altitude. Funding: Mayo Clinic & The North Face.

BACKGROUND Psycho‐socio stressors may over time result in dominance of the sympathetic nervous system (SNS) over the parasympathetic nervous system (PNS). Reduced PNS control over cardiovascular processes has been associated with decreased health. Heart rate variability (HRV) has been proposed as a technique to quantify SNS and PNS interactions and thus might offer a noninvasive predictive index. OBJECTIVE To investigate the impact of real‐life stressors on HRV fluctuations in independent living elders (EL). METHODS For three months every two weeks EL (N=22; Age=75±9; M/F ratio=17/5) performed autonomic tests consisting of quiet breathing, paced breathing and hand grip. All did a questionnaire assessing depression, positive/negative live events, and isolation. RESULTS Negative events (r=0.36, p=.01) and isolation (r=0.35, p=0.02) are correlated with HR. Personal changes in HRV, SDNN (r=−0.43, p<0.005) and Poincare Width (r= −0.42, p<0.005), are correlated to negative life events. CONCULSION Negative life events reduce HRV which suggests either SNS activation and/or PNS withdrawal. Research was made possible by Healthy for Life, TNO, and the Center for Innovation, Mayo Clinic.

BACKGROUND Exposure to high altitude (HA) results in sympathetic nervous system (SNS) activation. This might interact with HA related illness. HRV is a technique to quantify SNS and parasympathetic nervous system (PNS) interactions and thus offers a noninvasive index in extreme environments. OBJECTIVE To quantify the changes in HRV in elite athletes (AT), acclimatized for 2 mo. at Everest base camp (BC) prior to summiting, relative to a control group (CT) (climbing and acclimatizing to BC in 3 wks). METHODS AT (N=4, Age=35±10 y, BMI=22±2, M/F ratio 2/2) and CT (N=8, Age=35±10 y, BMI=26±2, M/F ratio 8/0) performed autonomic tests consisting of quiet breathing, paced breathing prior to, mid‐way at BC and at 2 wks post expedition. RESULTS At BC, AT had (compared to CT) higher HR (p=0.07) and reduced HRV (SDNN, p=0.09). For AT and CT combined: measures of HRV were reduced at BC (SDNN, p=0.05, Poincare length, p=0.05) and remained below baseline 2 wks post climb (SDNN, p=0.01; PCL, p=0.01). CONCULSION HRV is reduced with HA exposure in both AT and CT and remains reduced 2 wks post exposure, suggesting either SNS activation and/or PNS withdrawal. FUNDING : Mayo Clinic & The North Face.

Background It is documented that cognitive performance can diminish with altitude, but the sensitivity of specific tests have not been investigated. Our objective was to assess and compare cognitive performance from several tests and relate this to quality of sleep and acute mountain sickness (AMS). Methods During an Everest expedition, 3 cognitive tests (Stroop, Trail Making, and a proprietary motor accuracy test) were used along with a questionnaire to assess sleep and AMS. Six athlete climbers and 9 core team members were assessed pre and post‐expedition and at several time points during the expedition (up to 17,500 ft). Results To normalize for individual differences, scores were assessed as % change from baseline. There was no difference in the variation between repeated attempts in a single testing session (0.19<p<0.87), demonstrating that each test was reproducible. There was no decrement in test scores with altitude, nor was there an association with reported sleep quality. The Stroop performance was associated with AMS (p<0.05) and trending with headache (p< 0.15). The in‐house motor test trended towards an association with AMS and headache (p<0.15). However, the trail making test was not associated with AMS/headache. Conclusion With appropriate acclimatization, cognitive performance is maintained at altitude but is linked to presence of headache and AMS. Mayo Clinic and TNF.

BACKGROUND High altitude (HA) exposure influences appetite, protein synthesis and breakdown, and aerobic capacity. Thus, HA exposure typically causes weight (wt) loss, while the impact on aerobic capacity upon return to sea level is more variable. OBJECTIVE To examine the influence of hypobaric hypoxia on body composition and exercise capacity in elite HA climbers (n=4, 2 female) acclimating at ≥5,150 m over 2 mo. relative to trekkers (n=8, 0 female) acclimating at 5,150 m over 2 wks (Mt. Everest, Nepal). Each elite climber successfully summited Mt. Everest. METHODS Body composition (DEXA, skin folds, wt) and exercise capacity (treadmill) were assessed before and within 2 wks post HA. RESULTS HA exposure increased Hct and Hb, with peak values of 52±5% and 18±2 g/dl, and 50±3% and 17±1 g/dl for the climbers and trekkers, respectively. HA decreased lean and fat tissue in both the climbers (lean −4.4±2.3%, fat −8.2±4.0%) and trekkers (lean −1.8±1.6%, fat −5.8±6.1%) (all P ≤0.06). No change was observed in skin folds for either group. Wt decreased in the climbers (−5±2%, P <0.03) and trekkers (−3±1%, P <0.01). There was no change in VO 2max pre‐to post‐HA in either group (climbers 3.26 ± 0.37 vs. 3.27 ± 0.61 L/min; trekkers 3.60 ± 0.54 vs. 3.66 ± 0.43 L/min). CONCLUSION HA results in both lean and fat tissue loss in well acclimatized climbers and trekkers with little subsequent impact on aerobic capacity. Mayo Clinic & TNF.

The steadily growing elderly population calls for efficient, reliable and preferably ambulant health supervision. Since cardiovascular risk factors interact with psychosocial strain (e.g., depression), we investigated the potential contribution of psychosocial factors in discriminating generally healthy elderly from those with a cardiovascular condition, on and above routinely applied physiological assessments. Fifteen elderly (aged 60 to 88) with a cardiovascular diagnosis were compared to fifteen age and gender matched healthy peers. Six sequential standardized lab assessments were conducted (one every two weeks), including an autonomic test battery, a 6-min step test and questionnaires covering perceived psychological state and experiences over the previous two weeks. Specific combinations of physiological and psychological factors (most prominently symptoms of depression) effectively predicted (clinical) cardiovascular markers. Additionally, a highly significant prognostic model was found, including depressive symptoms, recently experienced negative events and social isolation. It appeared slightly superior in identifying elderly with or without a cardiovascular condition compared to a model that only included physiological parameters. Adding psychosocial parameters to cardiovascular assessments in elderly may consequently provide protocols that are significantly more efficient, relatively comfortable and technologically feasible in ambulant settings, without necessarily compromising prognostic accuracy.